🟢 Peridot Optics Lab: Refractive Index 1.654-1.690, Dispersion and Brilliance of a Cut Peridot

Peridot ((Mg,Fe)2SiO4): refractive index 1.654-1.690, Mohs hardness 6.5-7, dispersion 0.02. Peridot is the gem variety of olivine, a magnesium-iron silicate, and it is always some shade of yellow-green because iron is part of its chemical formula. It has a refractive index of about 1.65 to 1.69, Mohs hardness 6.5 to 7 and the unusually high birefringence of 0.036, which makes the back facets look doubled.